Field of the Invention
The present invention relates to a flame retarded epoxy resin composition, which is characterized by that said flame retarded epoxy resin composition comprising A) at least one type of epoxy resin and (B) a phosphorus-and-nitrogen-containing heterocyclic compound having a moiety which can react with the epoxy group of the epoxy resin and useful as a hardening agent for epoxy resin.
The flame retarded epoxy resin composition mentioned above can reach the standard for flame retarded property of UL94V-O without containing conventional flame retarded materials such as halides, antimony trioxide and the like. Thus, the said resin composition with excellent flame retarded properties is suitably used as the heat-resistant or flame-retarded materials required in the manufacture of electronic products, electric products, and automobile parts, and for other related applications.
While to the well known conventional epoxide has a limited usage range due to its combustible character, it has been known that the flame retarded property can be improved by adding resins containing halogen or haloalkyl group to the epoxide. In order to improve the flame retarded property of polymers or compositions thereof, flame retarded materials such as halo-organic compounds or oxides containing antimony or vanadium have traditionally been widely used to form high heat resistant compositions, however, the addition of such halo resins or polymers or metal (such as antimony) oxide is required in large amounts to attain the requirements for the flame retarded property.
Due to easy processability, high safety, and excellent mechanical and chemical properties, epoxy resins have been widely used in many fields, for example, in the application of composite material, such as coating, electrical insulation, construction, building materials, adhesives or laminated products. Further, now epoxy resins also can be used to make laminated plates for having strong adhesion to reinforcement materials (such as glass-fiber fabric) and no volatile elements formed and small shrinkage in hardening. On the other hand, laminated plates produced by epoxy resins have been massively applied to the component materials for electrical and electronic products and their other components.
In addition to a requirement to produce accurate and fine patterns on circuit boards, laminated plates are required to have excellent electrical properties, mechanical properties, and heat resistant processabilities for the currently significant manufacturing process of the printed circuit board. Most of widely used FR4 laminated plates or resin-coated copper foil for build-up process have a glass transition temperature of about 130xc2x0 C. after hardening. In the manufacturing process of the printed circuit board, the temperature is over 200xc2x0 C. during cutting and drilling, and even over 270xc2x0 C. during welding, which may make laminated plates break or crack during the manufacturing process. Therefore, various resins which possess high heat stability and high glass transition temperature have been developed. In addition, for the laminated plates of printed circuit board, another important property is flame retardancy, which is absolutely necessary in some applications such as in airplanes, automobiles, and other items of public transportation.
In order to impart the flame retarded property to the material for laminated plates, substances that put out flames and decrease burning should be introduced. For the laminated plates of epoxy resin/glass-fiber systems (or organic fiber) or dielectric materials for build-up process, generally halogen-containing compounds, particularly bromine-containing epoxy resins and hardeners, are added in combination with flame retardants, such as diantimony trioxide and the like, to achieve the strict flame retarded standards (as the UL94V-0 level) in the laminated plates. The flame retarded substance in epoxy resin usually required to contain up to 21% of bromine, is used in combination with diantimony trioxide or other retardants to attain the standard of UL 94V-0. However, it is harmful to human health for using high contents of bromine in epoxy resin or diantimony trioxide. Additionally, toxic smokes of erosive free radicals and hydrogen bromide generated by bromine burning, and also toxic furan bromides and a dioxine bromide compound produced from aromatic compounds with high bromine contents during burning seriously affect human health and the environment. Accordingly, it is most urgent to find a novel flame retarded material and a method to provide flame retarded properties to solve the pollution and environmental problems caused by the current use of laminated products or components containing bromide or bromo-epoxy resin. Especially, corresponding to the massive use of FR4 epoxy glass fiber laminated plates for electronic and electric products and components, it is necessary to actively develop flame retarded epoxy resin materials which will not endanger human beings and are environmentally protective.
Recently, in order to protect human health and decrease the sources of environmental pollution, various new flame retarded materials have been developed, wherein the technique is widely accepted for using phosphorus-containing compounds instead of those conventionally used flame retarded materials such as bromine-containing compounds. Currently phosphorus system compounds have been extensively studied and applied as the new generation of flame retarded materials with environmental-protective concepts. For example, red phosphorus or phosphorus-containing organic compounds (such as triphenyl phosphate, triphenylmethyl phosphate, etc.) are directly added to substitute halide compounds as a flame retarder to improve the burning property of polymer materials or hardening resin materials. However, addition of such flame retarded compounds in large amounts direct into resins is always required to achieve the effect of flame retardancy. Due to the smaller molecular weight of the compound, higher migration will affect the properties of resin substrates, for example, to worse electrical properties, adhesive strength, heat resistance, etc., and result in difficulty in application.
Later techniques using a reactive type of phosphorus-containing epoxy resin instead of bromine-containing or bromo-epoxy resins generally used as flame retarded ingredients have been developed. For example, in U.S. Pat. No. 5,376,453, laminated plates, which are produced by using a composition of phosphates with epoxy groups and nitrogen-containing hardening agents, need to be added with various phosphate-containing epoxy resins to increase phosphorus content to achieve the strict burning standard of UL 94V-0. In U.S. Pat. No. 5,458,978, a composition formed from epoxy phosphates, nitrogen-containing epoxy resin, and metal complex hardener is used to make laminated plates which have a glass transition temperature of about 175xc2x0 C. and a flame retarded property similar to that of UL 94V-0 (42 seconds, 50 seconds related to critical value). In U.S. Pat. Nos. 4,973,631 and 5,086,156, a trialkyl oxide having an active hydrogen substituent (such as an amino group) is used alone or in combination with other amine hardeners to harden epoxy resins; by means of such a hardening method to introduce phosphorus to resins, however, a proper flame retarded effect can not be achieved due to the lower content of phosphorus; and there is no actual measurement of the flame retardant effect in these two patents. According to the techniques disclosed in the above patents, it is realized that addition of various or high contents of phosphorus-containing compounds is usually required to meet the flame retarded standard, however, various additional additives usually make the processing conditions of products difficult to control or the quality of products inferior.
Therefore, the method to increase flame retarded property employs a nitrogen- and phosphorus-containing substance instead of traditional bromine- or antimony-containing substances.
In accordance with environmental problems generated by flame retarded materials previously added with toxic substances containing halogens or antimony, the inventor of the present invention has developed a flame retarded compound corresponding to the environmentally protective requirements. The said compound is a phosphorus- and nitrogen-containing heterocyclic compound, and structurally has a moiety reactive with the epoxy group of an epoxy resin, and can be used as a hardener component of the epoxy resin composition.
According to the present invention, it has been found to increase the heat resistance of the epoxy resin composition by adding effective amounts of phosphorus- and nitrogen-containing heterocyclic compounds to epoxy resin. Besides having improved flame retarded properties, the epoxy resin composition-formed by the foregoing phosphorus- and nitrogen-containing compound and the epoxy resin can also have the effect of increasing electric and mechanical properties, and have excellent processing properties. Accordingly, the production cost can be reduced because no large amount of flame retarded additives is required. In addition, such flame retarded resin compositions having a high glass transition temperature and excellent heat resistance are suitably used for production of prepregs with flame retarded properties, laminated layers, dielectric materials for build-up process and materials for printed circuit boards.